Mark Wagner is Vice President and General Manager, Wheel End Division, at Consolidated Metco (ConMet). After receiving a bachelor of science in mechanical engineering from The University of Toledo in Ohio

Wheel Ends

Q

What makes a premium seal "premium"?

Posted by Ed
from Michigan
on Tue, 2014-08-05 16:17

A

Seals have a tough life, being the sole rubber part in a world of metal. That means contaminants like metal debris, dirt, and even liquids can have a bigger impact on seals than on other components. Heat and cold also impact these guys more than the metal parts. A small seal leak can be an indication that something more substantial is wrong in the wheel end, long before failure of other internal parts occurs.

Truck wheel seals have two important functions: keep the lubricant inside the hub and keep contaminants, like water and dirt, out. Simple enough. For many years hub seals were something of an afterthought, being replaced often as part of routine brake maintenance. But in the early 1990s we saw the emergence of premium seals that proposed to solve some of the failures caused by contamination and improper installation, as well as to extend the life of the seals.

Much like bearings, a seal's expected service life depends on maintaining the environment it runs in. That means keeping it from being damaged at installation, avoiding overheating, and keeping it clean and lubricated throughout its life. To some degree, we can design seals and systems that avoid installation damage, but many factors influence the running temperatures and contamination effects. Even the most robust seal will still be affected by improper handling. Try submerging your truck in water. It’s not a submarine, you know.

Premium seals today have two main differences from earlier products:

Materials that can withstand higher temperatures

Sophisticated exclusion features, or secondary protection.

Beyond that, seals must endure in environments like busy, loud, and sometimes dirty assembly plants and/or maintenance garages where mechanics are under enormous time constraints. Even when a mechanic does his or her work perfectly, outside influences can impede proper installation and maintenance.

Materials in premium seals can be very costly—sometimes four or more times the cost of basic polymers. These materials are harder and therefore wear more slowly and can offer longer life, but they are also more difficult to mold and trim. That means quality control takes on added importance (and expense).

The main sealing lips of the seals are generally molded rubber with a spiral-wound spring that causes the seal lip to follow the contour of the seal journal in conditions of deflection and vibration. Secondary protection features consist of labyrinths, closed caps with small gaps, flingers, and additional seal lips intended to keep contaminants out. Labyrinths are difficult to rate, but suffice it to say you want a tortuous path for any splash water or other contaminant to have to pass through to get to the seal. If you can make stuff fling out using two closely rotating parts, all the better.

How do you know if you have a good seal or not? At a minimum, it should have the features described above. Equally important, though, is how well the seal has held up under testing, both in a laboratory and in the field, where they are so many more variables.

The best way to maintain your seals is to keep the lubricants clean and replenished, and inspect for leaks as often as you can. Inspections should be done by drivers during pre-trip and at Preventive Maintenance intervals, which can vary depending on the conditions you run in. The more severe the conditions, the shorter the intervals should be. ConMet, like most manufacturers and the Technology Maintenance Council (TMC), recommends similar inspections for bearings, so at least you get two for one on your inspections.